# Lesson 10

Subtraction Algorithms (Part 3)

### Lesson Purpose

The purpose of this lesson is for students to use a subtraction algorithm that records a single digit for the difference between the numbers in each place value position and a condensed notation for a decomposed hundred or ten.

### Lesson Narrative

In this lesson, students continue to learn how to use algorithms to subtract within 1,000. The new algorithm in this lesson draws attention to how place value can be used to record less digits in each place value position. This condensed notation also changes the steps of the algorithm because students don't write the numbers in expanded form to start or add up the partial differences at the end.

• Representation
• MLR8

Activity 1: A New Subtraction Algorithm

### Learning Goals

Teacher Facing

• Relate subtraction algorithms to one another using place value understanding.
• Subtract numbers within 1,000 using another algorithm based on place value.

### Student Facing

• Let’s learn another algorithm to subtract.

### Required Materials

Materials to Gather

### Lesson Timeline

 Warm-up 10 min Activity 1 20 min Activity 2 15 min Lesson Synthesis 10 min Cool-down 5 min

### Teacher Reflection Questions

Who got to do math today in class and how do you know? Identify the norms or routines that allowed these students to engage in mathematics. How can you adjust these norms and routines so all students do math tomorrow?